Vauxhall Vectra engine jerking at low seeds

try a fuel filter 1st, thats to much dosh to spend on a hunch.

What fuel do you use? where do you buy it from?
iif its a supermarket, change to a good Quality fuel say BP Ultimate, try redex or millers thru it a bottle to half a tank say.

If none of this changes anything, id check for dirt in fuel tank / fuel pipes. Doubt it will be the pumps.

Wont cost much to try these, the best of luck to you

Does it do it in and out of turbo?
definatley only between 30 - 50mph? 3rd gear?

if the "chugging" is at light to medium throttle the problem will probably something to do with your egr system or throttle flap if its fitted very very unlikly to be your fuel pump. also check the wiring from the main ecu this is located inside the front left arch liner they suffer from wiring faults as the loom has a nice u shaped water trap where the loom passes under the chassis.

just a thought check the linjage on intake manifold if you remove the engine cover you should be able to see a matal bar linking small arms, they become detached and could cause your problem.